Transfer of Streptococcus lactis and Related Streptococci to the Genus Lactococcus gen. nov.

Nucleic acid hybridization studies and immunological relationships of superoxide dismutase demonstrated that Streptococcus lactis (and its subspecies), Lactobacillus xylosus, Lactobacillus hordniae, S. garvieae, S. plantarum and S. raffinolactis are closely related to each other but not to other streptococci. Therefore we propose that these taxa be transferred to a new genus Lactococcus gen.nov. as Lactococcus lactis subsp. lactis (including former S. lactis subsp. diacetilactis and Lactobacillus xylosus) comb.nov., L. lactis subsp. cremoris comb.nov., L. lactis subsp. hordniae comb.nov., L. garvieae comb.nov., L. plantarum comb.nov. and L. raffinolactis comb.nov. The relatedness of these organisms has also been demonstrated by the similarity of their lipoteichoic acid structures, lipid pattern, fatty acid and menaquinone compositions. Motile ‘S. lactis’ strains are not genetically related to the lactococci although they possess the group N antigen. They also differ in their lipid composition from lactococci and may represent a new taxon. A description of the genus Lactococcus and emended descriptions of the corresponding species are given. The main characteristics for the differentiation of lactococci are listed in Table 8.